Recently, an illumination sensor that detects ambient brightness is mounted on a liquid crystal panel of an electronic apparatus such as a cellular phone or a digital camera in order to control ht emission amount of a backlight of the liquid crystal panel in accordance with the illumination of disturbance (light such as sunlight or a fluorescent lamp). Further, demands that proximity sensor is mounted have been increasing in order to reduce power consumption, for example, in order to turn off display in a case where a face approaches the liquid crystal panel in the liquid crystal panel of the electronic apparatus such as a cellular phone or a digital camera. In addition, in recent years, an integrated proximity-illumination sensor in which a proximity sensor and an illumination sensor are integrated has been suggested for a demand for size reduction of the electronic apparatuses.
Analog types of the illumination sensors and the proximity sensors have been the mainstream in related art. However, digital types are common because high resolution is requested recently. Further, a spectral characteristic close to visual sensitivity is requested for the illumination sensor. Consequently, the illumination sensor is requested to be an analog-digital conversion circuit that performs analog-digital conversion for an input current and performs an output and to realize the spectral characteristic close to the visual sensitivity in a simple configuration.
In the integrated proximity-illumination sensor, in order to improve a proximity characteristic, a resin in an upper portion of a light-receiving element is formed into a lens shape, and a directional characteristic is thereby improved. Further, because a reflected light amount from a housing panel of a cellular phone becomes noise, reduction in the noise light amount from housing reflection has to be devised. In this case, there is a problem in that the directional characteristic becomes narrow because the lens is present in the upper portion of the light-receiving element in the integrated proximity-illumination sensor in an illumination sensor action. Further, in a case where the integrated proximity-illumination sensor is mounted on the electronic device such as a cellular phone and where the incident angle of light fluctuates due to hand movement or the like, a problem occurs in that the illumination value fluctuates. Thus, a sensor has to be suggested in which the directional characteristic is wide and the illumination value does not fluctuate even in a case where the lens is present in the upper portion of the light-receiving element.
Here, a description will be made about a scheme for satisfying the above requests. As an illumination sensor in which sensitivity does not depends on the angle of irradiation light, a scheme disclosed in PTL 1 has been suggested. In this scheme, a light shielding unit is provided in which the light transmittance in a central portion is lowest and the light transmittance concentrically and gradually becomes higher toward the outside.
Meanwhile, as an illumination sensor in which the sensitivity does not depends on the angle of irradiation light, a scheme disclosed in PTL 2 has been suggested. In this scheme, light-receiving sensitivity adjustment means is provided in which lowering in the light-receiving sensitivity around a peak is made large compared to lowering in the other light-receiving sensitivities.
Next, FIG. 15 illustrates a configuration in which a sensor output is converted to a digital value by using an analog-digital conversion circuit and the digital value is thereafter subtracted, as an example of an illumination sensor in related art. A current input to a photodiode (PD) 1 with a spectral characteristic of an infrared region is set as an input current Iin1, and a current input to a PD 2 with a spectral characteristic of a visible region to the infrared region is set as an input current Iin2.
The result of analog-digital conversion of the input current Iin2 by ADC2 is set as ADCOUT2, and the result of analog-digital conversion of the input current Iin1 by ADC1 is set as ADCOUT1. ADCOUT1 is multiplied by a by a multiplier and is subtracted from ADCOUT2 by a subtractor, and the same result as a scheme disclosed in PTL 3 may thereby be obtained.ADCOUT2−ADCOUT1*α=Iin2−Iin1*α
As for the illumination sensor, a scheme has become common in which light such as sunlight or a fluorescent lamp is converted to a current by a PD and a digital output is performed by an integration type analog-digital conversion circuit. As for the proximity sensor, a scheme that includes the integration type analog-digital conversion circuit and a driving circuit of a light-emitting diode has been employed in recent years.
FIG. 13 illustrates a configuration of a common proximity sensor. This proximity sensor includes a PD, a light-emitting diode (LED), and a control circuit. The LED is driven from the control circuit, conversion to a current is performed by the PD for light reception, and detection is performed by the control circuit. The difference between the data in the period in which the LED is driven (Data1) and the data in the period in which the LED is not driven (Data2) is set as proximity data (Data1−Data2). In a case where a detection object is present, reflected light from the detection object is intense. Thus, as illustrated in FIG. 14(a), the current of the PD becomes high and exceeds a threshold value Data_th of the control circuit, and a determination is made as proximity. In a case where no detection object is present, reflected light from the detection object is weak. Thus, as illustrated in FIG. 14(b), the current of the PD is low and does not exceed the threshold value Data_th of the control circuit, and a determination is thus made as non-proximity. In this case, the reflected light amount from the housing panel of the cellular phone, which is indicated by the broken line arrows in FIG. 13, becomes noise. Thus, the reduction in the noise light amount from the housing reflection has to be devised.